Saturday, 27 June 2020

A Bilateral Gynandromorph

On opening the trap this morning, amongst the usual suspects was a Poplar Hawk-moth, not uncommon in my trap but when moving it out I noticed something unusual. To cut a long story short it is a Bilateral Gynandromorph! That means that one side of the moth is male and the other side is female, in this case the left side is male and the right side is female.
When the egg cell or ovum is fertilised by the sperm it forms a single cell which would normally develop into the caterpillar and so on. The usual pattern of cell division 2, 4, 8, 16 occurs until certain cells start to differentiate at a different rate to form nerve cell, gut cells and so on. In a Bilateral Gynandromorph the first cell division produces the usual two cells but something has happened to the sex chromosomes during this cell division and the resulting two cells each have a different arrangement one male and one female! The two cells produced normally go on and produce the left hand and the right hand halves of the moth so the same happens here and the moth ends up one side male and one side female.

Here endeth the first lesson. Once a Biology teacher always...."

I was asked the question "How often does it happen?

"I suspect with the size of your average moth and the fact that with things like Heart and Darts where all you are doing is counting them plus the fact that many moths do not show any sexual dimorphism (ie male and female look the same) it is not spotted that often even when it does happen. The antennae as seen here may be the best place to see feather male as against plain female, but even that it is not obvious at first sight with this Poplar Hawkmoth. It is only when you look at the antennae carefully or through photographs that you see that they are, in fact, different. I know in many of the older Butterfly books photographs of Gynandromorphs sometime appear, the Orange Tip or Blue butterflies are favourites again more easy to see."  Martyn Davies


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